The present invention is directed to polymer compositions having anti-fouling activity, particularly polymer compositions suitable for marine and fresh water applications.
Biofouling presents a severe operational problem to aquaculture for example. On fish cages, it restricts water flow through netting which reduces the supply of dissolved oxygen and the removal of excess feed and waste products. In suspended shell-fish culture, a large mass of fouling can compete with the cultured species for food and space, and can overwhelm flotation capacity. Current metal-based antifoulants are undesirable for aquaculture because of possible adverse environmental effects, and consumer concerns that may jeopardise market image. Commercially available, but biodegradable compounds, or naturally occurring antifoulants extracted from marine organisms, may provide an acceptable solution by offering broad spectrum activity, and in the case of natural antifoulants, acting via chemical deterrence rather than toxicity.
Commercialisation of antifouling technology other than paints is still in its infancy, and few field trials are reported in the literature. Although there are many antifouling agents and compositions presently available, the methods typically used to protect an object from fouling in an aqueous environment involve applying some form of protective coating to the surface of the object. Unfortunately, this approach is not suitable for all applications and there is a need for other means of protecting such objects from microbial- or macro-fouling. The present inventors have developed new polymer compositions that contain antifouling agents which have surprising broad-spectrum antifouling characteristics over prolonged periods and at lower concentrations than were previously believed possible.
In a first general aspect, the present invention consists in a polymer composition having antifouling activity, the composition including a polymer and an organic antifouling agent, and having broad-spectrum antifouling activity for a prolonged period of at least 100 days when substantially immersed in a natural aqueous environment.
The polymer may be any polymer suitable for preparation by extrusion processes known to the art. In particular, polymers containing ethylene-vinyl acetate copolymer (EVA), high-density polyethylene (HDPE), nylon, polypropylene (PP), sodium ionomer, copolymer of ethylene and acrylic acid, or mixtures thereof are suitable. The present invention has been particularly successful using EVA, HDPE polymers, or mixtures thereof. It will be appreciated, however, that other polymers or mixtures may also be suitable to produce antifouling polymer compositions with prolonged and broad-spectrum antifouling activity according to the present invention.
The antifouling agents suitable for the present invention are synthetic antifouling agents belonging to the families of isothiazolones, furanones, or combinations thereof. Examples of suitable isothiazolones and furanones are shown in FIG. 1. Preferably, the isothiazolone antifouling agent is 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one produced and sold by Rohm and Haas under the name Sea-Nine 211(trademark).
Preferably, the furanone antifouling agent is a mixture of the halogenated furanones referred herein as 26/27 or 33/34 where
26 is (1xe2x80x2RS,5E)-3-(1xe2x80x2-Bromoethyl)-4-bromo-5-(bromomethylidene)-2(5H)-furanone;
27 is (1xe2x80x2RS)-3-(1xe2x80x2-Bromoethyl)-5-(dibromomethylidene)-2(5H)-furanone;
33 is (1xe2x80x2RS,5Z)-3-(1xe2x80x2-Bromohexyl)-4-bromo-5-(bromomethylidene)-2(5H)-furanone; and
34 is (1xe2x80x2RS)-3-(1xe2x80x2-Bromohexyl)-5-(dibromomethylidene)-2(5H)-furanone.
In a preferred embodiment of the first aspect of the present invention, the antifouling agents are used at a concentration of about 0.1 to 20%, more preferably from about 1 to 10% (w/w) of polymer composition. It will be appreciated that mixtures of antifouling agents (natural, synthetic, or commercial) may also be used to prepare the polymer compositions according to the present invention.
When using the antifouling agents in the form of isothiazolones or furanones, the present inventors have made the surprising discovery that in use the polymer compositions release amounts of the agent that would not be expected to prevent fouling by organisms. Release studies found that the activity was caused by about ten-fold less of the agent than what has been shown previously. The compositions that had good and persistent activity over a prolonged period released less than 5, and in several cases less than 1 xcexcg/cm2/day of the agent. Preferably, these release rates are obtained.
The polymer compositions according to the present invention had significant antifouling activity when tested in marine environments. Preferably the antifouling activity lasts for at least 100 days, more preferably at least 200 days, and even more preferably at least 300 days.
It will be appreciated that the use of the term natural aqueous environment is meant to include oceans, estuaries, lakes, ponds, rivers and aqueous environments where microorganisms (bacteria) or macroorganisms (algae, plants, invertebrates or other taxa) are known to cause fouling, or there is the potential for such fouling.
The polymer compositions according to the present invention can be made by any known means but preferably made by extrusion or molding processes. The distinct advantage of this form of manufacture is that there is the possibility of controlling or manipulating the type of composition produced. For example, fibers may be produced that can be woven into nets, ropes and the like for use in the aquaculture industry. Also, solid structures can be extruded or molded in the form of cages, crates or structural materials for use in aqueous environments. Moreover, the extrusion or molding processes result in efficient blending of the polymer and active ingredient, a factor influencing the low release rates observed by the present inventors.
It will be appreciated that the present invention is not restricted to use in aquaculture applications. Any situation in aqueous conditions where there is a problem of fouling may be applicable. For example, pipes and plumbing equipment may be made from the polymers according to the present invention.
In a preferred form, the present invention consists in a polymer composition having broad-spectrum antifouling activity comprising a polymer selected from the group consisting of ethylene-vinyl acetate copolymer (EVA), high-density polyethylene (HDPE), sodium ionomer, copolymer of ethylene and acrylic acid, and mixtures thereof and one or more organic antifouling agents selected from the group consisting of antifouling agents belonging to the families of isothiazolones, furanones, and combinations thereof, wherein in use the polymer has broad-spectrum antifouling activity for a prolonged period of at least 100 days, preferably at least 200 days, more preferably at least 250 days, and most preferably for at least 300 days when the composition is substantially immersed in a natural aqueous environment, preferably a marine environment.
In a further preferred form, the present invention consists in an antifouling polymer composition comprising a polymer and an isothiazolone or one or more furanone antifouling agents or mixtures thereof, the composition capable of maintaining broad-spectrum antifouling activity in an natural aqueous environment, preferably a marine environment, by releasing less than about 3-5 xcexcg/cm2/day of the antifouling agent over a period of greater than 100 days, preferably over 200 days.
The initial release rates of the antifouling agents from the polymers in the first few days of exposure to an aqueous environment were much higher than the values listed above. What was surprising was the finding that after this initial high release rate, there was sustained antifouling activity (greater than 100 days) of the polymers according to the present invention caused by release of very low levels of antifouling agents.
In a second aspect, the present invention consists in the use of the antifouling compositions according to the first aspect of the present invention in the preparation of extruded or molded articles having sustained broad-spectrum antifouling activity for at least 100 days when substantially immersed in a natural aqueous environment.
In a third aspect, the present invention consists in the use of an isothiazolone or one or more furanone antifouling agents, in the manufacture of an antifouling polymer composition having broad spectrum antifouling activity for at least 100 days when the polymer is substantially immersed in a natural aqueous environment.
In a fourth aspect, the present invention consists in an article made from a composition according to the first aspect of the present invention, the article having broad spectrum antifouling activity for at least 100 days when substantially immersed in a natural aqueous environment.
Throughout this specification, unless the context requires otherwise, the word xe2x80x9ccomprisexe2x80x9d, or variations such as xe2x80x9ccomprisesxe2x80x9d or xe2x80x9ccomprisingxe2x80x9d, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
In order that the present invention may be more clearly understood, preferred forms will be described with reference to the following examples and the accompanying drawings.